Multi-layer thermal insulation, for example, for insulating so-called re-entry vehicles are generally known in various embodiments. Such multi-layer insulation achieves a considerably increased thermal insulation compared to a single layer insulation having same weight as the multi-layer insulation.
Conventional applications of such multi-layer insulation involve static pressure conditions, for example, for use near the earth's surface or alternatively in a vacuum (conventional satellite multilayer insulation). These conditions do not apply to re-entry spacecraft. During re-entry of a spacecraft into the earth's atmosphere the pressure in a multi-layer insulation varies, dependent upon the spacecraft flight altitude, whereby the thermal conductivity of the insulation increases due to the presence of gases contained in the multi-layer insulation. For example, at a certain flight altitude and for a certain arrangement and selection of specific insulation layers half of the total thermal conduction through the multi-layer insulation may be due to the thermal conduction by the gases contained in the multi-layer insulation.
For typical re-entry trajectories the maximum aerodynamic heating of the spacecraft occurs at relatively high flight altitudes, for example 75 to 65 km and correspondingly low pressures. On the other hand, at lower flight altitudes and correspondingly higher pressures, the outer skin of the spacecraft is heated to a much lower extent or is even cooled.
All of the previously known embodiments of multi-layer thermal insulation have either a relatively high weight or are relatively thick so that they increase either the total weight of the spacecraft or also not insignificantly increase the total dimensions of the spacecraft. In other words, by applying relatively thick insulation layers onto the fuselage skin of the spacecraft, either the outer dimensions of the craft are increased or the usable interior space of the craft is decreased.
U.S. Pat. No. 4,344,591 discloses a high temperature multiwall thermal insulation system comprising sandwich panels with flat and dimpled metal foils. Between the outer panels and the inner panel an intermediate fiber insulation as e.g. Johns Manville's microquartz mat having a density of 72 kg/m.sup.3 is provided. The thermal insulation system of said U.S. Patent is also characterized by a disadvantageous weight.